Scientists have devised a clever form of bug-to-bug combat to fight Chagas' disease, a potentially fatal muscle infection transmitted by the aphidlike kissing bug. The new weapon is a bacterium, normally found in the bug's gut, that is engineered to produce a lethal protein. The altered bacterium, described in tomorrow's Proceedings of the National Academy of Sciences, might help prevent Chagas', a scourge that kills about 45,000 people a year in South and Central America. It could also provide a model approach against other insect-borne diseases.

A team at Yale University, Rockefeller University in New York City, and the Centers for Disease Control and Prevention in Atlanta engineered a strain of the bacterium Rhodococcus rhodnii, which lives in the gut of the kissing bug, to produce an insect antibiotic called cecropin A. The researchers exploited an unappetizing feeding habit of kissing bugs--they eat each other's feces--by peppering faux feces with the engineered bacteria. The bugs lapped it up. Once inside, the bacterial Trojan horse began pumping cecropin A into the kissing bug's bowels, which are also home to Trypanosoma cruzi, the culprit behind Chagas' disease. The cecropin A kills the trypanosomes but leaves the insects unharmed.

"It's fantastic," says Thomas Miller, an entomologist at the University of California, Riverside. "It changes the way we think about things." Besides kissing bugs, he says, this technique might be used to hijack a variety of other insect disease vectors, from mosquitoes that transmit malaria to deer ticks that transmit Lyme disease. Yale team member Frank Richards agrees: "It's a general principle that can be used in many systems."

One potential problem is that T. cruzi could quickly develop resistance to cecropin A: "If you try treating anything with single-agent therapy, resistance develops quite rapidly," says Yale team member Ravi Duravasula. He and his colleagues are probing for ways to overcome potential resistance, such as by getting the R. rhodnii to churn out a second antibiotic. In the meantime, the researchers are putting the altered bacterium through its paces in a controlled field test in sealed huts in Guatemala.